The present invention relates to an apparatus and method for conditioning a polishing pad. More particularly, the present invention relates to an apparatus and method for conditioning a polishing pad used in the chemical mechanical planarization of semiconductor wafers.
Semiconductor wafers are typically fabricated with multiple copies of a desired integrated circuit design that will later be separated and made into individual chips. A common technique for forming the circuitry on a semiconductor is photolithography. Part of the photolithography process requires that a special camera focus on the wafer to project an image of the circuit on the wafer. The ability of the camera to focus on the surface of the wafer is often adversely affected by unevenness in the wafer surface. This sensitivity is accentuated with the current drive toward smaller, more highly integrated circuit designs. Semiconductor devices are also commonly constructed in layers, where a portion of a circuit is created on a first level and conductive vias are made to connect up to the next level of the circuit. After each layer of the circuit is etched on a semiconductor wafer, an oxide layer is put down allowing the vias to pass through but covering the rest of the previous circuit level. Each layer of the circuit can create or add unevenness to the wafer that is preferably smoothed out before generating the next circuit layer.
Chemical mechanical planarization (CMP) techniques are used to planarize the raw wafer and each layer of material added thereafter. Available CMP systems, commonly called wafer polishers, often use a rotating wafer holder that brings the wafer into contact with a polishing pad moving in the plane of the wafer surface to be planarized.
In some CMP systems, a fixed-abrasive polishing pad is used to polish the wafer. The wafer holder then presses the wafer against the rotating fixed-abrasive polishing pad and is rotated to polish and planarize the wafer. CMP systems using a fixed-abrasive pad require the presence of features on the semiconductor wafer to function. Fixed-abrasive pads include abrasive particles embedded within a polymer matrix. To operate a CMP system having a fixed-abrasive pad, the fixed-abrasive pad must first be conditioned. Traditionally, fixed-abrasive pads are conditioned by polishing a patterned semiconductor wafer. The patterned semiconductor wafer conditions the fixed-abrasive pad by using the topography features created by the etching and deposition processes on the semiconductor wafer to remove a portion of the polymer matrix, thus exposing the abrasive particles embedded within. By exposing abrasive particles within the polymer matrix, the fixed-abrasive pad can begin to polish the semiconductor wafer.
In other CMP systems, a polishing fluid, such as a chemical polishing agent or slurry containing microabrasives, is applied to a wet-abrasive polishing pad to polish the wafer. The wafer holder then presses the wafer against the rotating wet-abrasive polishing pad and is rotated to polish and planarize the wafer. During the polishing process, the properties of the wet-abrasive polishing pad can change. Slurry particles and polishing byproducts accumulate on the surface of the pad. Polishing byproducts and morphology changes on the pad surface affect the properties of the polishing pad and cause the polishing pad to suffer from a reduction in both its polishing rate and performance uniformity. To maintain a consistent pad surface, provide microchannels for slurry transport, and remove debris or byproducts generated during the CMP process, wet-abrasive polishing pads are also typically conditioned. Pad conditioning restores the wet-abrasive polishing pad""s properties by re-abrading or otherwise restoring the surface of the polishing pad. This conditioning process enables the pad to maintain a stable removal rate while polishing a substrate or planarizing a deposited layer and lessens the impact of pad degradation on the quality of the polished substrate.
As used herein, the term xe2x80x9cpolishing padxe2x80x9d will be used to describe not only fixed-abrasive polishing pads, but also wet-abrasive polishing pads as well.
Generally, polishing pads are either linear or radial in shape. A linear polishing pad is mounted on a linear belt that is wrapped around a series of rollers. A radial polishing pad is mounted on a circular disc that rotates about an axis.
One present method for conditioning a polishing pad uses a rotary disk embedded with diamond particles to roughen the surface of the polishing pad.
Typically, the disk is brought against the polishing pad and rotated about an axis perpendicular to the polishing pad while the polishing pad is rotated. The diamond coated disks produce predetermined microgrooves on the surface of the polishing pad. Because the linear velocities of the leading, center and lagging portions of the disk are different, the rate of microgrooving is different. This non-uniform microgrooving has led some pad conditioner manufacturers to add a continuous oscillation motion to the rotational movement of the rotary disk pad conditioners. This extra movement can result in part of the wafer being exposed to freshly conditioned portions of the polishing pad and another part of the wafer being exposed to a used portion of the polishing pad.
Another apparatus and method used for conditioning a polishing pad implements a rotatable bar on the end of an arm. The bar may have diamond grit embedded in it or high pressure nozzles disposed along its length. In operation, the arm swings the bar out over the rotating polishing pad and the bar is rotated about an axis perpendicular to the polishing pad in order to score the polishing pad, or spray pressurized water on the polishing pad, in a concentric pattern. These types of pad conditioners often do not provide uniform pad conditioning because they are only applied to a small portion of the width of the polishing pad""s surface at any given time. Thus, the pressure of the conditioner against the polishing pad can vary.
Accordingly, further development of an apparatus and method for conditioning a polishing pad, and more specifically, for conditioning a polishing pad used in the chemical mechanical planarization of semiconductor wafers, is necessary in order to provide uniform pad conditioning.
According to a first aspect of the present invention, an apparatus for conditioning a polishing pad used in chemical mechanical planarization of semiconductor wafers is provided. The polishing pad travels in a forward direction, and has a first point traveling at a first velocity and a second point traveling at a second velocity. The conditioning apparatus includes a non-rotatable conditioning member configured to engage the polishing pad. The conditioning member includes a primary edge opposed to a secondary edge. The first point defines a first path across the conditioning member from the primary edge to the secondary edge as the first point travels in the forward direction. The first path has a first length. The second point defines a second path across the conditioning member from the primary edge to the secondary edge as the second point travels in the forward direction. The second path has a second length. The second path does not intersect with the first path. Finally, the value of the first velocity multiplied by the first length is substantially equal to the value of the second velocity multiplied by the second length.
According to another aspect of the present invention, a method for conditioning a polishing pad used in chemical mechanical planarization of semiconductor wafers is provided. The method includes providing a non-rotatable conditioning member configured to engage the polishing pad. The conditioning member includes a primary edge opposed to a secondary edge, wherein the primary edge and the secondary edge are both in contact with the polishing pad, and wherein the primary edge is generally parallel to the secondary edge. The method also includes moving the polishing pad in a forward direction, and pressing the conditioning member against the polishing pad.